1. Field of the Invention
This invention relates generally to orthodontic appliances and more particularly to an orthodontic palatal arch wire capable of accurately transmitting correctional forces to a pair of brackets mounted on opposing molars.
2. Description of the Prior Art
A palatal arch wire is employed by orthodontists to apply corrective forces to misaligned molars by exerting directional control over the pair of brackets to which it is attached; each bracket being mounted on an opposing molar for transmission of the corrective forces therethrough to the tooth. The types of forces desirably exerted include expansion, contraction, intrusion, torquing and/or rotating.
Considerations present in developing a suitable palatal arch wire include the ease of adequately attaching each of the end portions to a corresponding molar bracket and the ease of removal therefrom. The desire for easy removal of the arch wire from the bracket deters the use of certain forms of attachments, such as soldering, welding, or crimping of the bracket around the wire.
A problem that arises with the use of palatal arch wires is the inadequate control over the brackets resulting from the improper anchorage of the wire to the brackets. Thus, this problem occurs when corrective forces produced by the arch wire are not fully transmitted therethrough to each of the brackets because of motional slippage between the wire and brackets. For example, untransmitted angular movement or rotation of the wire relative to a bracket occurs when the bracket utilizes an open-ended tube having a circular bore therethrough as a receptacle for a similarly dimensioned circular arch wire. The wire can twist or rotate freely within the tube when a torquing force is applied through the arch wire. Corrective forces are efficiently produced in arch wires having compressible loops or spring devices intermediate their lengths; however, until the present invention these arch wires have provided certain disadvantages, with respect to their form of anchorage to the molar brackets.
The problem of motional slippage in palatal arch wires has been recognized in the prior art. Examples of patents addressing this problem are U.S. Pat. No. 3,162,948 to Gerber and U.S. Pat. No. 3,792,529 to Goshgarian. Gerber, in the aforesaid patent, provides for a palatal arch wire capable of contracting or spreading the dental arch by means of a spring device. The arch wire is inserted near each of its ends into a tube attached to a mounting bracket. Gerber suggests inserting an arch wire having a polygonal shape into an open-ended hollow tube that has a mating polygonal cross-sectional bore. This permits interengagement and a torsional locking arrangement, so as to prevent angular movement about the longitudinal axis of the tubes.
The arch wires described in the aforesaid patent to Goshgarian have an adjustable U-shaped integral compressible loop intermediate its length. In addition, the terminal ends of the wire are bent over double to form rectangularly shaped inserts. Goshgarian suggests frictionally fitting each of these inserts into the bracket opening and relying on the springlike quality of the arch wires to cause the inserts to be firmly retained therein, thereby minimizing the twisting of the end portions within the bracket.
Each of these structures, Gerber's and Goshgarian's, for securing the arch wire to the bracket provides disadvantages. The use of a polygonally shaped wire and tube capable of interengagement requires fabrication of these items within relatively small dimensional tolerances to achieve the desired locking arrangement. Similarly, the rectangularly shaped insert requires a specially fabricated receiving member on the band to frictionally engage the unconventional terminal end. This frictional engagement is responsible for the production of undue force in the tooth during insertion and removal of the insert from the receiving member.
Thus, there is a need for a palatal arch wire, having a circular cross-sectional dimension, that is easily attachable to, and yet easily removable from, a receiving member having a circular bore therethrough; while at the same time, being capable of preventing motional slippage of the wire relative to the bracket during securement.
Accordingly, it is a principal object of this invention to provide for an arch wire capable of being easily attached to a pair of brackets in such a manner that the correctional forces produced by the arch wire are precisely applied therethrough to the teeth without slippage of the arch wire relative to the bracket.
It is a further object of the present invention to provide a molar bracket that cooperates with the palatal arch wire for accurate transmission of the correctional forces.
It is another object of the present invention to provide for a simply manufactured arch wire which is easily attachable to, and removable from, the molar bracket.
An additional object of the present invention is to provide an arch wire that is inexpensive to manufacture and has widespread applicability.